Inorg. Chem. 1995,34, 214-217
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Kinetics of H2 Dissociation from Some Iridium-Dihydrogen Complexes with Structurally Different (H2) Ligands Vladimir I. Bakhmutov," Evgenii V. Vorontsov, and Alexey B. Vymenits Institute of Organo-Element Compounds, Russian Academy of Sciences, 117813 GSP-1, 28 Vavilova, Moscow, Russia. Received May 26, 1994@
The variable-temperature 'H NMR spectra permit the determination of AH" (-7.1 kcdmol) and AS" (-16.0 eu) for formation of trans-IrH(H2)C12(PhJ'3)2from IrHCl2(PPr'3)2and H2 in toluene-d8. The (H2) ligand of the related complex trans-IrH(Hz)C12(PCy3)2 was characterized by a TI& value of 3.4 ms at 200 MHz using TI measurements for dissolved H2 in the presence of IrHC12(PCy3)2. Analysis of the variable-temperature lH NMR spectra and T1 measurements resulted in estimation of the rate, AH$ and A 9 for H2 dissociation from both trans- and cis-IrH(H2)C12(PPr$)2 and IrH2(Hz)X(PP&)2 (X = C1, Br) in toluene-dg. The rate of H2 loss decreases dramatically from lo5 to >/T1(r2(H2>)(2) H2 in the presence of IC,Tl(H2) and T1(q2(H2)) are relaxation times of free HZ and the (H2) ligand, and P are corresponding mole fractions determined from positions of the averaged Hz signal and the signals of free and coordinated H2. It is important that eq 2 can be used when the life time of the (H2) ligand t(q2(H2))
